Increasing the land and labor productivity by enlarging the size of paddyfields is the main purpose of land consolidation works. In large-sized paddy fields the naturalsoil and water productivity varies, resulting in differences in yield from place to place.The heterogeneity of soil properties and fertility, non-uniformity in ponding water properties, and crop yield in a large-sized paddy field (2.14 ha) were evaluated. Measurementswere made in a 25m, two-dimensional grid of 24 points. Field surface elevation was measuredbefore planting. Topsoil properties measured on the grid were bulk density, moisturecontent, texture, soil strength, pH, hydraulic conductivity and soil nitrate nitrogen. Plantheight was measured as a growth factor four times during the crop season and also after harvest.Shoot dry matter weight, grain weight and number of grains were measured after harvest.Ponding water depth of the field and rainfall received at the site were recordedthroughout the crop growing season.
The coefficient of variation of shoot dry matter weight and grain yield were more than35%, greater than that of canopy height. High productivity sites had 3.4 times more yieldthan low productivity sites. Among the soil properties measured on the grid, hydraulic conductivityhad the highest coefficient of variation, 101.3%, followed by residual soil nitratenitrogen, 52.7%. Although no apparent soil structure was found in crop yield, a regressionrelation was found between soil texture, fertility and ponding water depth and crop yield.Laboratory studies using 1/2000 a Wagner's pot were conducted with heterogeneous soilsto develop corrective measures. From the experimental results, it is suggested that soildressing and variable rate fertilization can be used to reduce the influence of field level heterogeneityin order to get maximum uniform yield in large-sized paddy fields.

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The solutions of boundary value problems involving strain-softening materialproperty are full of serious difficulties from both the viewpoint of modeling of strain- localization and the viewpoint of numerical and mathematical procedures. A realistic soilmodel is applied to capture the shear band formation in plane strain compression (PSC) tests on dense sand with a very high angle of internal friction. The model is based on experi- mental findings about the inherent and induced anisotropies involved in sand. Stress- dilatancy relation is considered through non-associated plastic flow. Mesh size-dependenthardening modulus is considered to alleviate the mesh size-dependency of the solution. Inthe simulations a shear band formed without the introduction of any physical defects. It isfound that the inevitable numerical precision error is sufficient to trigger the formation ofa shear band. Different mesh sizes, the advantage of symmetry and boundary conditions aretested numerically while checking the formation of the shear band. It is found that meshsize, domains taken for the analysis, and boundary conditions have profound effects on theformation of shear band in PSC tests. The results of simulation are compared with thosefrom physical experiments.

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Optimum farm machinery selection may reduce production costs considerably.In doing this, one has to take into account the size of the farm, the distribution of cropsand crop rotation, cultural practices used throughout the year, farm machinery technical dataand consumption costs for each operation. Moreover one has to take into account soil, cropand weather characteristics in order to reach a reliable prediction of the suitable days forfield work throughout the year, which inevitably impose a time restriction in farm machineryoperations. In the present work, linear programming was employed as a mathematicaltool for providing the right selection of farm machinery, based on minimizing machineryoperational costs, taking into consideration all above mentioned interrelated factors and constraints.
For 400 ha of agricultural land, allocated for the cultivation of 4 different crops (wheat200 ha, corn 100 ha, alfalfa 50 ha and beans 50 ha), considering four different tractor sizes (44, 56, 76, and 148 kW), it was found that optimum agricultural machinery selection wouldinclude four 76 kW tractors and two 44 kW tractors.

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Across the Lower Mekong Basin, a number of areas suffer from frequent inundation, hindering social and economical development of the region. To relieve the damage caused by such inundation and to ensure stable agricultural production, continuousassessment of the damage is necessary. Damage conditions are currently surveyed by interviewing farmers; however, data gathered by this method are not sufficient to implement effective measures after water recession. To improve this situation, we decided to developsystems of inundation mapping utilizing Remote Sensing (RS) technology and theGeographic Information System (GIS).
At the beginning of the development, we selected the area along the Mekong River in LaoPDR as the pilot area. Within the pilot area, we have implemented surveys on GPS reference points and lateral and longitudinal cross measurements in major inundation regions.We installed instruments for observation of meteorology and hydrology, also reflectors thatconfirm water depth through satellite images. Furthermore, we utilized RADARSAT, which has a synthetic aperture radar enabling penetration of rain clouds to take images ofground inundation situation, and which is able to take images of specific area repeatedlywithin a few days. As a result, it has become possible to create an inundation map by overlayingtime-series inundation images.

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We used a model of a stratified paddy field (plow layer, plowsole, and subsoil) with gravel under the plowsole of the type that exist in volcanic ash areas beside floodplains. These models were planted with rice and were fertilized. The models were usedto investigate the removal of soluble ions in percolation water under different percolationpatterns: open system percolation and closed system percolation.
The results are as follows.
In the case of high drainage levels, plow layer, plowsole and subsoil became a closed systempercolation and were made into reduction layers. But in the case of low drainage levels, only the subsoil became an open system percolation and was made into an oxidationlayer. Concentrations of nitrate ion, nitrite ion, iron ion, manganese ion and dissolved oxygenin water of the closed system percolation increased more than those in the open system.Potassium ion concentrations in plow layer and plowsole increased during the 50 days fromthe start of examination over its initial concentration in the subsoil. Concentration of the totalnitrogen in drainage was higher than that in inundation during 60 days as well as that oftotal phosphorus over 30 days. After these periods, the two concentrations were nearlyequal.

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